Aluminum salts, such as aluminum chlorohydrex (also called aluminum chlorohydrex polymeric salts and abbreviated here as “ACH”) and aluminum zirconium glycine salts (abbreviated here as “ZAG”, “ZAG complexes” or “AZG”), are known to contain a variety of polymeric and oligomeric species with molecular weights (MW) of 100 Da-500,000 Da.
In an attempt to increase the quality and quantity of smaller aluminum and/or zirconium species, a number of efforts have focused on: (1) how to select the components of ACH and ZAG that affect the performance of these materials; and (2) how to manipulate these components to obtain and/or maintain the presence of smaller types of these components. These attempts have included the development of analytical techniques to identify the components. Size exclusion chromatography (“SEC”) or gel permeation chromatography (“GPC”) are methods frequently used for obtaining information on polymer distribution in aluminum salt solutions. With appropriate chromatographic columns, generally five distinctive groups of polymer species can be detected in commercial ACH and ZAG complexes appearing in a chromatogram as peaks 1, 2, 3, 4 and a peak known as “5,6”, referred to hereinafter as Peak 5. Peak 1 contains the larger Zr species (greater than 60 Angstroms). Peaks 2 and 3 contain larger aluminum species. Peak 4 contains smaller aluminum species (aluminum oligomers, or small aluminum clusters) and has been correlated with enhanced antiperspirant efficacy for both Al and Al/Zr salts. Peak 5 contains the smallest and most acidic aluminum species. Various analytical approaches for characterizing the peaks of ACH and various types of ZAG actives are found in “Antiperspirant Actives—Enhanced Efficacy Aluminum-Zirconium-Glucine (AZG) Salts” by Dr. Allan H. Rosenberg (Cosmetics and Toiletries Worldwide, Fondots, D. C. ed., Hertfordshire, UK: Aston Publishing Group, 1993, pages 252, 254-256).
Attempts to activate antiperspirant salts to produce materials having improved efficacy have included developing processes for obtaining composition having large amounts of Peak 4.
Solutions of partially neutralized aluminum are known to contain a variety of hydrolytic Al species. The identity and distribution of these various forms depends on the hydrolysis ratio (i.e. the OH:Al molar ratio), the Al precursor and the choice of the reaction condition. In the field of antiperspirant (AP) technology, SEC chromatography is the traditional method used for elucidating the distribution of these Al species. Conventional SEC physically separates Al species into domains which are subsequently measured using a concentration detector. It is generally recognized that at least five domains of Al species can be differentiated by size-exclusive chromatography. These domains are commonly referred to Peak 1, Peak 2, Peak 3, Peak 4, and Peak 5, where increasing peak number indicates smaller relative size of the eluting species. Peak 4 and Peak 5 have been implicated as highly efficacious Al domains for antiperspirants. Monomeric Al and low oligomers, are known to elute under Peak 5. Oligomeric polyhydroxyoxoaluminum cations elute under Peak 4.
It is well known in the art that such a variety of hydrolytic Al species exists and that it is possible to distinguish large aqueous aluminum hydroxide molecules using spectroscopic methods such as 27Al NMR which elucidates the structural environment surrounding Al atoms which are embodied in various forms (Casey W H, “Large Aqueous Aluminum Hydroxide Molecules”, Chem. Rev. 2006, 106 (1), pages 1 to 16).
There are two regions in a 27Al NMR spectrum that represent Al nuclei which are octahedrally coordinated (0 ppm-60 ppm) and tetrahedrally coordinated (60 ppm-90 ppm). The octahedral region is exemplified by the hexa-aqua Al species, i.e. monomeric Al, which resonates sharply at 0 ppm. The tetrahedral region is exemplified by sharp resonance at 62.5 ppm from the Al13 polyhydroxyoxoaluminum cation. Al13 is composed of 12 octahedrally coordinated Al atoms surrounded by one centrally-cited Al atom which is tetrahedrally coordinated. The Al30 polyhydroxyoxoaluminum cation is essentially a dimer of the Al13 polyhydroxyoxoaluminum cation and contains 2 tetrahedrally coordinated Al atoms which resonate at 70 ppm.
It is known that 27Al NMR spectroscopy may not fully elucidate the chemical composition of a partially neutralized Al salt solution, since there may be a variety of Al species that do not give rise to sharp and unambiguous resonance peaks. These species can be considered as effectively NMR-invisible. Unless the 27Al NMR spectroscopy is carried out quantitatively, the relative concentration of these NMR-invisible species cannot be determined and must be inferred from SEC chromatography.
The state of the art discloses a number of methods for synthesizing and purifying the Al13 polyhydroxyoxoaluminum cation (for example Fu G, et al. “Aging Processes of Alumina Sol-Gels; Characterization of New Aluminum Polycations by 27Al NMR Spectroscopy” Chem. Mater. 1991, 3(4), pages 602 to 610).
It is known that the Al13 polyhydroxyoxoaluminum cation may be convened to obtain the Al30 polyhydroxyoxoaluminum cation by heating a solution of the Al13 polyhydroxyoxoaluminum cation (Roswell J et al, “Speciation and Thermal Transformation in Alumina Sols; Structures of the Polyhydroxyoxoaluminum Cluster [Al30O8(OH56(H2O)26]18+ and its δ-Keggin Moieté”, J. Am. Chem. Soc. 2000, 122, pages 3777 to 3778; Chen Z et al, “Effect of thermal treatment on the formation and transformation of Keggin Al13 and Al30 species in hydrolytic polymeric aluminum solutions”, Colloids and Surfaces A: Physiochem. Eng. Aspects, 292 (2007) pages 110 to 118; and Allouche L et al, “Conversion of Al13 Keggin ε into Al30: a reaction controlled by aluminum monomers”, Inorganic Chemistry Communications, 6 (2003) pages 1167-1170).
Heating an Al13 solution is the only synthetic pathway to achieving Al30 which has been described in the literature. As well as the references identified above, WO-A-2006/103092 and Shafran K L et al, “The static anion exchange method for generation of high purity aluminum polyoxocations and monodisperse aluminum hydroxide nano-particles”, J. Mater. Chem., 2005, 15, pages 3415 to 3423, disclose the use of an ion-exchange process to synthesize Al13 to achieve greater than 90% purity, and disclose heating the thus-formed Al13 solution to form Al30.
Partial neutralization of Al salts have been shown to yield trace quantities of the polyhydroxyoxoaluminum cation detectable at 76 ppm by 27Al NMR. There is a need in the art for a high-yield synthetic route to the polyhydroxyoxoaluminum cation detectable at 76 ppm by 27Al NMR. The small quantities obtained, lack of purity, and lack of method of making has prevented science from isolating this polycation in sufficient quantity and purity so that its structure could be determined.
It would be desirable to develop a method to make a composition containing a polyhydroxyoxoaluminum cation detectable at 76 ppm by 27Al NMR in a sufficient quantity so that this cation can be analyzed for chemical structure and physical properties. Such a method could make a composition that has the polyhydroxyoxoaluminum cation detectable at 76 ppm by 27Al NMR present in a relative abundance that is greater than any other species of aluminum detectable by 27Al NMR.